Gas Separation Applications Research Articles

Heterostructured hybrids of metal–organic frameworks (MOFs) and covalent–organic frameworks (COFs)

MOF/COF-based hybrids show the properties of precisely tunable compositions and structures, and provide a broad range of potential applications in gas sorption and separation, catalysis, energy transfer, biomedicine, etc.

Theoretical Studies of Metal-Organic Frameworks: Calculation Methods and Applications in Catalysis, Gas Separation and Battery

Theoretical Studies of Metal-Organic Frameworks: Calculation Methods and Applications in Catalysis, Gas Separation and Battery

Triphenylene containing blue-light emitting semi-fluorinated aryl ether polymers with excellent thermal and photostability

Integration of polycyclic aromatic hydrocarbon (PAH) units into semi-fluorinated polymers affords high thermal stability and excellent processability for potential applications in optoelectronic, gas-separation, and advanced composites.

Stimuli-Responsive of Magnetic Metal-Organic Frameworks (Mmofs): Synthesis, Dispersion Control, and its Tunability into Polymer Matrix Under the Augmented-Magnetic Field for Gas Separation Applications

Stimuli-Responsive of Magnetic Metal-Organic Frameworks (Mmofs): Synthesis, Dispersion Control, and its Tunability into Polymer Matrix Under the Augmented-Magnetic Field for Gas Separation Applications

Synthesis of Polyimides Containing Tröger's Base and Tetramethyl-Substituted Triphenylmethane Moieties with Tunable Fractional Free Volume for Gas Separation Application

Synthesis of Polyimides Containing Tröger's Base and Tetramethyl-Substituted Triphenylmethane Moieties with Tunable Fractional Free Volume for Gas Separation Application

Phthalide-containing poly(ether-imide)s based thermal rearrangement membranes for gas separation application.

The diamine monomer 3,3-bis[4-(3-hydroxy-4-amino-phenoxy)phenyl]phthalide (BHAPPP) was firstly synthesized by the nucleophilic substitution of 5-fluoro-2-nitrophenol and phenolphthalein, followed by a reduction reaction. A series of phthalide-containing poly(ether imide)s (PEI) were then prepared through the polycondensation of BHAPPP with six kinds of dianhydrides, including 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic dianhydride (ODPA), 1,2,3,4-cyclobutane tetracarboxylic dianhydride (CBDA) and pyromellitic dianhydride (PMDA), as well as thermal imidization. After further thermal treatment, the corresponding thermal rearrangement (TR) membranes were obtained. Due to the existence of the phthalide lactone ring, the PEIs probably underwent TR and crosslinking simultaneously. With the increase of thermal treatment temperature, the mechanical properties of the TR membranes dramatically decreased, but the gas separation properties obviously increased. When the PEIs were treated at 450 °C for 1 h, the CO2, H2, O2, N2 and CH4 permeability of TR(BHAPPP-6FDA) reached 258.5, 190.5, 38.35, 4.25 and 2.15 Barrers, respectively. Meanwhile, the CO2/CH4 selectivity of 120.2 sharply exceeded the 2008 Robeson limit, and O2/N2 selectivity was 9.02, close to the 2015 upper limit. Therefore, the TR membranes derived from phthalide-containing PEIs exhibit superior gas separation performance, andare expected to be applied in the field of gas separation.

Single-gas and mixed-gas permeation of N2/CH4 in thermally-rearranged TR-PBO membranes and their 6FDA-bisAPAF polyimide precursor studied by molecular dynamics simulations

High-performance polymers with polybenzoxazole (PBO) structures, formed via thermal rearrangement (TR) of aromatic polyimide precursors, have been developed for gas separation applications. The present work compares the transport of N2 and CH4 in a 6FDA-bisAPAF polyimide precursor and in its TR-PBO derivative using molecular dynamics (MD) simulations. The modelling closely mimicked the experimental approach by transforming a 6FDA-bisAPAF atomistic model into its corresponding TR-PBO structure via a specific algorithm. The densities and void spaces of both precursor and TR polymers were found to compare well to experimental data. An iterative technique was used to obtain the single-gas sorption isotherms of N2 and CH4 at 338.5 K in both polymers over a range of feed pressures up to and exceeding 65 bar. CH4 was systematically found to be more soluble than N2. Solubilities in both matrices were quite similar with those in TR-PBO being slightly higher due to its larger fraction of significant volume. Volume dilation analyses confirmed a higher resistance to plasticization for TR-PBO. Extended single-gas N2 and CH4 simulations and 2 : 1 binary CH4/N2 mixed-gas simulations were then conducted in both matrices at 338.5 K and at a pressure of ∼65 bar corresponding to natural gas processing conditions. Mixed-gas sorption was modelled using a modification of the aforementioned iterative method, which fixed the pressure and iterated to convergence the number of molecules of each type of penetrant. The gas diffusion coefficients were estimated using the Trajectory-Extending Kinetic Monte Carlo (TEKMC) procedure. As found experimentally, significantly higher diffusivities and permeabilities were observed in the TR polymer, which led to a slightly lower ideal N2/CH4 permselectivity for TR-PBO (∼2.6) when compared to its 6FDA-bisAPAF precursor (∼3.8). However, both models showed a reduced N2/CH4 separation efficiency under 2 : 1 binary CH4/N2 mixed-gas conditions bordering on the loss of selectivity. For 6FDA-bisAPAF, both permeabilities decreased in the mixed-gas case, but more for N2 than for CH4. For TR-PBO, the permeability of the faster N2 decreased while the permeability of the slower CH4 increased under mixed-gas conditions. This confirms that single-gas simulations are not sufficient for the prediction of the actual mixed-gas permselectivity behaviour in such polymers.

MOF-based MMMs breaking the upper bounds of polymers for a large variety of gas separations

• Permeabilities of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases were reported for 5599 MOFs. • 181,249 types of MOF/polymer MMMs were studied for 11 different gas separations. • A large number of MOF/polymer MMMs exceeded the upper bounds of polymers. • A guideline was provided for selection of the best MOF-polymer combinations. Mixed matrix membranes (MMMs) are a strong alternative to the conventional polymeric membranes which suffer from a trade-off between selectivity and gas permeability. Considering the existence of a large number of metal–organic frameworks (MOFs) and polymers, computational screening of MOF/polymer MMMs is strongly desired to explore their upper limits in various gas separation processes before experimental efforts. In this work, we computed permeability of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases in 5599 metal organic frameworks (MOFs) using atomically-detailed simulations and then assessed performances of >180,000 different MOF/polymer MMMs for 11 different gas separations He/H 2 , He/N 2 , He/CH 4 , N 2 /CH 4 , H 2 /N 2 , H 2 /CH 4 O 2 /N 2 , CO 2 /N 2 , CO 2 /CH 4 , H 2 /CO 2 , He/CO 2 . Our results revealed that many MOF/polymer MMMs exceed the upper bounds due to their high gas permeability and/or selectivity. The impact of MOFs on the separation performances of polymers was examined to provide guidelines for the best MOF-polymer pairing for a variety of gas separations. Data showed that using MOFs as fillers significantly improves the permeability of CO 2 , CH 4 , N 2 , O 2 , H 2 , and He gases in 41 different types of polymers without changing their selectivities. Many MOFs offer a great opportunity for MMM applications by improving both the permeability and selectivity of polymers such as of Teflon AF-2400 for N 2 /CH 4 , PTMSP-co(95/5) for H 2 /CH 4 , PTMSDPA for O 2 /N 2 and PTMSP for CO 2 /CH 4 separations. The best MOF fillers leading to MMMs with exceptional selectivities were found to have narrow pores and low porosities. These results will contribute to directing the experimental efforts to the best MOF/polymer MMM materials for numerous industrially important gas separation applications.

Achieving a stable COF with the combination of “flat” and “twist” large-size rigid synthons for selective gas adsorption and separation

A new type of covalent organic framework (COF) was achieved using combination of structrally rigid and conformationally othorganal building blocks. The N-2-aryl-substituted triazole derivative (NAT-CHO) was prepared with co-planar conformation among the three aromatic rings as the “flat” building block. The 4,4′,4′′,4′′′-(ethene-1,1,2,2-tetrayl)tetraaniline) (ETTA) was applied as the “twist” building block. A 2D sheet of network was obtained through imine formation. The resulting NAT-COF gave excellent thermal and chemical stability, survived aqueous solutions from pH 5 to 13. With large-size building blocks, the porous framework NAT-COF gave efficient gas adsorption with excellent selectivity of C3 propane over C1 me-thane, suggesting its potential application for selective gas capture and separation.

Facile synthesis of Bi-functionalized intrinsic microporous polymer with fully carbon backbone for gas separation application

Membrane technology is considered as one of the most efficient methods to capture CO2 economically. In which, functionalized PIMs are attracting more and more attention due to their superior gas separation properties in both high permeability and selectivity; however, one of the biggest challenges is their high cost. Herein, a novel bi-functionalized PIM with fully carbon main chain was synthesized efficiently by a simple one-step Friedel-Craft polycondensation reaction. The HSBI-NO2 polymer bearing two functional groups (–OH and –NO2) derived from two cheap raw materials is easy scale up, which showed high molecular weight of 94 KDa, good solubility in most conventional solvents, and high thermal stability with on-site decomposition temperature above 344 °C. There is no glass transition temperature below 300 °C that confirmed the rigidity of this polymer backbone. It also showed modest microporosity with BET surface area of ∼ 288 m2 g−1 and strong mechanical strength of 65 Mpa. The HSBI-NO2 membrane demonstrated an over 3-fold improved CO2 permeability than previously reported analogue without sacrificing its CO2/CH4 selectivity due to the bulky and rigid spirobisindane contortion center. Temperature dependent gas separation analysis indicated that the gas permeation in HSBI-NO2 was attributed to its diffusion, as confirmed by its much higher activation energy of diffusion (Ed) than heat of adsorption (-ΔHs). HSBI-NO2 also showed good anti-plasticization properties, aging resistance, and CO2/CH4 mixed-gas separation performance. Even under the upstream CO2 partial pressure of 10 bar, the permeability of CO2 is 52.3 Barrer and the CO2/CH4 selectivity is still 20. The convenient in synthesis, cheap raw materials, good physical properties, and modest to high separation performance make this HSBI-NO2 polymer extremely cost-effectiveness and great potential in practical gas separation applications.

Polymers of intrinsic microporosity and thermally rearranged polymer membranes for highly efficient gas separation

• PIMs and TR polymers are referred to polymers with a highly microporous structure. • The major challenge of PIMs and TR polymers is achieving a high permselectivity. • We studied the monomer molecular design of energy-efficient PIM/TR based membranes. • Different methods for synthesizing PIMs and TR polymers are described. • The presence of functional/pendant groups such as are investigated. • Different strategies for preparation and tailoring of their properties are discussed. In the last decades, many novel polymeric materials have been considered to prepare highly energy-efficient gas separation membranes. There is a continuous search to overcome the trade-off relationship between the gas permeability and selectivity to improve the membrane separation performance during long-term operation. One of the most important research fields of molecular design and polymer chemistry is the synthesis of new polymers with a highly microporous structure, referred to as polymers of intrinsic microporosity (PIMs) and thermally rearranged (TR) polymers. The major challenge of PIMs and TR polymers, required for their application in membrane gas separation, is achieving a high permeability and selectivity, which remain stable over prolonged periods and under all possible operating conditions. Limits of their use can be low mechanical stability, sophisticated and challanging synthesis methods, physical aging of PIMs, etc. For TR polymers, identifying the optimum temperature in the thermal treatment process is challenging, and the preparation of thin-film TR membranes from PBO precursor via conventional methods is difficult. Moreover, the productivity of the membrane modules and the adhesion between the support/polymer and nanomaterials/polymer need to be improved in mixed matrix membranes (MMMs). Also, the formation of defects in the membrane structure is the main challenge to overcome for the fabrication of thin-film composites (TFCs). In this manuscript, we carefully review the molecular design and the properties and performance of PIMs and TR materials as energy-efficient membranes for various gas separations, emphasizing CO 2 /CH 4 and CO 2 /N 2 . Different methods for synthesizing PIMs and TR polymers are described, and the resulting polymers are evaluated for gas separation. Structure designing for the synthesis of PIMs and TR membranes and the influence of different chemical structures of monomers for creating chain rigidity by non-planar groups, and tuning the angle of contorted centres, are investigated. Moreover, the presence of functional groups and other substituents, such as fluorinated, sulfonated, carboxylic, tetrazole, and other groups, are investigated. Different strategies for membrane preparation and tailoring of their properties, such as cross-linking, co-polymerization, blending with other polymeric or organic and inorganic materials, are discussed as well.

Gas processing with intrinsically porous 2D membranes

The importance of membranes for the processing of gases with significant technological as well as environmental impact is rapidly increasing given their advantages in operation, low energy consumption, and efficiencies. In this work we employ density functional theory calculations to investigate the performance of a number of intrinsically porous two-dimensional (2D) membranes for gas separation applications. Our results indicate that gases with small kinetic diameters such as He, H2O, Ne, H2, and CO2 present low energy barriers and high permeability through these membranes, in contrast to other components of natural and atmospheric gases. Additionally, we show that some of the studied membranes present high selectivities for a number of permeating gases. Our results indicate that these materials are promising candidates for applications in gas processing such as natural gas dehydration and sweetening, He recovery, O2 and N2 production from air, H2 purification, and CO2 capturing.

Modulating Polymer Dynamics via Supramolecular Interaction with Ultrasmall Nanocages for Recyclable Gas Separation Membranes with Intrinsic Microporosity.

The engineering of mixed-matrix membranes is severely hindered by the trade-off between mechanical performance and effective utilization of inorganic fillers' microporosity. Herein, we report a feasible approach for optimal gas separation membranes through the fabrication of coordination nanocages with poly(4-vinylpyridine) (P4VP) via strong supramolecular interactions, enabling the homogeneous dispersion of nanocages in polymer matrixes with long-term structural stability. Meanwhile, suggested from dynamics studies, the strong attraction between P4VP and nanocages slows down polymer dynamics and rigidifies the polymer chains, leading to frustrated packing and lowered densities of the polymer matrix. This effect allows the micropores of nanocages to be accessible to external gas molecules, contributing to the intrinsic microporosity of the nanocomposites and the simultaneous enhancement of permselectivities. The facile strategy for supramolecular synthesis and polymer dynamics attenuation paves avenues to rational design of functional hybrid membranes for gas separation applications.

Novel mixed matrix membranes (MMMs) based on metal–organic framework (MOF) [Mg3(BTC)2]/poly-ether sulfone (PES): preparation and application for CO2 gas separation

Novel mixed matrix membranes (MMMs) based on metal–organic framework (MOF) [Mg3(BTC)2]/poly-ether sulfone (PES): preparation and application for CO2 gas separation

Interface regulation of mixed matrix membranes by ultrathin MOF nanosheet for faster CO2 transfer

Mixed matrix membranes (MMMs) incorporating porous materials received extensive attention for applications of gas separation, but the one shows significant high permeability and increased selectivity is rare. Here, we report a strategy of interface regulation in two groups of MMMs via formed H-bonding by a newly designed and ultrathin metal organic framework nanosheet (MOFN). The chemically stable MOFN (thickness: 5–8 nm) with lamellae of micrometre lateral dimensions was prepared from [Hf6] cluster and tricarboxylate ligand, where the capping molecule of formic acid coordinates with Hf4+ ion as H-bonding donor toward incorporated polymers and also acts as an anisotropic regulator for MOFN growth. The well-distributed MOFN in two polymers shows sharply promoted CO2 permeability (720 GPU and 2085 GPU), as well as enhanced separation factor, over wide pressure and temperature ranges that are suitable for CO2 capture from natural gas. This is because the H-bonding regulated polymer-MOFN alignments lead to contractile channel and abundant porosity, validated by Raman mapping and positron annihilation lifetime spectroscopy. This work not only gives rise two candidate membranes for selective CO2 removal from naturals gas, but also, more prospectively, deliveries a design philosophy for construction of advanced MMMs.

Magnetic field-induced improvement in O2/N2 gas separation applications of simultaneously co-casted superparamagnetic mixed matrix membranes

For industrial purposes and current challenges facing the world, the selective separation of oxygen and nitrogen gases from the air by polymer mixed matrix membranes is crucial. Due to the diamagnetic nature of water molecules used in the fabrication of the polymer membranes, the magnetic field (H) may affect the resulting separation performance. Here, using a simultaneous co-casting method, empty and superparamagnetic Fe3O4 nanoparticle-filled double-layer polyethersulfone (PES)/Pebax®1657 mixed matrix membranes are fabricated under different external magnetic field intensities in the range of H = 0–5000 Oe. The O2 and N2 permeances of the PES/Pebax® membranes are found to increase with increasing the magnetic field intensity, arising from an enhancement in the polymer chain mobility. The Fe3O4 nanoparticles form thick root-like superparamagnetic channels on the double-layer PES/Pebax® surface at a magnetic field intensity of 4000 Oe, resulting in an O2/ N2 ideal selectivity of 3.59 at a feed gas pressure of 10 bar. This indicates an improvement of 40% in the selectivity compared to a single-layer Pebax® membrane filled with Fe3O4 nanoparticles.

Development of poly(ethylene glycol) diacrylate membrane for facilitated CO2/N2 separation

Carbon dioxide (CO2) is responsible for approximately 80% of greenhouse gases emission that is the main source to global climate change causing notable environmental impacts. Poly (ethylene glycol) diacrylate (PEGDA) have polar PEG repeating units, which provide a strong affinity towards carbon dioxide (CO2) molecules has been blended with 3-aminopropyltrimethoxysilane (APTMS) to synthesize membrane for CO2/nitrogen (N2) separation. The new synthesized membrane is studied for potential applications in gas separation and to be implemented in control CO2 emission. APTMS is also used to delay the diffusion between polymer and solvent. In this study, concentration of polymer of PEGDA and casting solvent of APTMS in terms of mol ratio from a range of 0.9:1.1 to 1.3:0.7 is discussed. Based on the results, PEGDA membrane shows best gas separation performance at mol ratio of PEGDA to APTMS of 1:1 where the permeance for both CO2/N2, and CO2/N2 selectivity are 75.21±0.15 GPU, 22.95±0.05 GPU and 3.28±0.12, respectively. An optimal aminosilane/polymer reaction ratio benefits the gas separation performance of the membrane due to the affinity of the membrane towards CO2 and formation of different membrane surface morphology.

Isosteric Heats and Entropy of Adsorption in Henry's Law Region for Carbon and MOFs Structures for Energy Conversion Applications

The thermodynamic property surfaces such as enthalpy and entropy of an adsorbate + adsorbent systems are essential for designing adsorption-assisted thermal compression, gas storage, separation, and other applications. This paper presents the enthalpy (∆ho) and the entropy (∆so) of the adsorbent-adsorbate system under the barrier of Henry's law region. Hence Henry's law coefficient and Gibbs analogy are applied to formulate the adsorption driving force (∆go). To justify the proposed formulation, the initial adsorption phenomena (at pressure, P → 0) of C2H5OH, CO2, CH4, N2, H2O, R125, R134a, R152a, and R1234yf on graphite/MOFs (such as Zr-MOF-801, Mg-MOF-74, and Al-Fumarate) are considered. It is found that the adsorption driving force is linked with the pore structure of adsorbent materials. We employ experimentally measured isotherms data to calculate the adsorption driving force, ∆go for various adsorbate + activated carbon/MOFs systems. The maximum adsorption driving force is found at the pore widths of 3 Å to 7 Å. The ∆go decreases with higher adsorbent-pore volume and depends on adsorbate molecule size. Employing the proposed driving force concepts, (i) the specific cooing, heating, and COP of the adsorption system, and (ii) the CO2/CH4 storage capacity in the adsorption cell can be projected and analyzed. The adsorption driving force relates to enthalpic and entropic interactions and is useful for the design of adsorbents and the selection of adsorbent-adsorbate pairs for gas storage, separation, and various energy-related applications.

Smart light-responsive hierarchical metal organic frameworks constructed mixed matrix membranes for efficient gas separation

One type of new light-responsive hierarchical metal organic framework (MOF) has been successfully prepared using Co(NO3)3·6H2O as the metal salt and 4,4′-azobenzenedicarboxylic acid as the ligand by microwave method for the first time. It is found that MOF [Co(AzDC)] exhibits a light-responsive characteristic to SO2 adsorption due to the presence of azo group from the ligand. The light-responsive hierarchical MOFs are incorporated into Matrimid® 5218 (PI) matrix to prepare mixed matrix membranes (MMMs) for gas separation application. The morphology, crystallinity, chain mobility and thermal stability of MMMs are explored. Results show that Co(AzDC) may elevate both the CO2(SO2) permeability and CO2(SO2)/N2 selectivity of the MMMs. In particular, the Co(AzDC) doped MMMs exhibit the significantly improved CO2(SO2)/N2 selectivity from 33 (123) for PI control membrane to 78 (420) for MMMs, overcoming the 2008 Robeson upper bound for CO2/N2 system. Size-sieving effect of Co(AzDC) with pore size 0.35 ​nm enhances the selectivity, while the –N=N– group from Co(AzDC) shows affinity to CO2 molecular rather than N2, also elevating selectivity of MMMs. In brief, enhanced selectivity of high-performance membrane is attributed to incorporation of Co(AzDC) particles, which displays synergistic effects both in size-sieving and CO2-philic interaction for CO2/N2 separation. Smart highly selective interface is constructed in MMMs by switching the configuration of MOFs from cis to trans. The SO2 permeability and SO2/N2 selectivity of MMMs are investigated under both visible light and ultraviolet light states, and the SO2/N2 separation performance under visible light is notably improved in comparison with that under ultraviolet light state.

Metal-organic Framework Materials Coupled to Optical Fibers for Chemical Sensing: A Review.

Metal-organic frameworks (MOFs), a newer class of crystalline nanoporous materials, have been in the limelight owing to their exceptional tunability for structures and physicochemical properties, and have found successful applications in gas storage, gas separation, and catalysis. The mesmerizing properties of MOFs, especially the extensive and tunable porosity and chemical selectivity, also make them an excellent candidate class as chemo-sensory materials. Moreover, MOF-based sensors have attracted considerable attention in the past decade. Recent literature reviews focused on the progress of MOF-based electronic sensors and luminescent MOF sensors, while sensors exploiting the dielectric properties (refractive index) of MOFs were also demonstrated and discussed very recently. The motivation of this report is to provide, for the first time, a general review on such MOF sensors with a particular focus on miniature optical fiber (OF) based MOF sensors and to demonstrate the promising potential of MOFs as dielectric coatings on OF for highly sensitive chemical sensing. The fundamental principle of OF-MOF sensors relies on the tunability of the refractive index of a MOF, which is dependent on the amount and type of adsorbed guest molecules in the MOF pores. MOF sensors based on different optical sensing principles are reviewed; challenges and perspectives on further research into the field of OF-MOF sensors are also discussed.